Gosh, Kazmcc!
A fan club of one!
Yes, 14 x 12 frames can be heavy to handle, esp if full of stores.
And a full 14 x 12 brood box is a pig to move. But how often is that necessary?
On the plus side, it's far easier to inspect than two BBs (double brood or brood and a half). Moreover, the volume is closer to what a normal colony needs, even at the height of summer. And in winter, if properly filled with stores, the colony has sufficient stores for a normal winter in one box, and there is less risk of the brood not getting to stores in a super. And, in spring, there's no need to try to find the queen in a cool spring, to confine her to the lower box.
Having said that, our RBI doesn't like it - but I've not found out why.
As for manipulating a full 14 x 12 frame, I find the method I was taught, is easy to do but difficult to describe. But it's designed to avoid putting strain on the hands and the wax, when flipping the frame horizontally, then upside down.
1) holding the frame normally by the lugs, move your right hand to your left, across close to your stomach, and move the left hand outwards and across to the right. You end up with arms crossed, with the frame the other way round.
2) Then, on the verticle plane, lift your right hand (and frame) upwards and back across. This twists the frame on its axis, so it ends upside down, in front of your face. The weight is taken by the side of the frame, not the field of wax.
3) Reverse to lower it.
I suggest practicing on a frame without bees!
Dusty